1. Field of the Invention
The present invention relates to a machine for lumber production that produces lumber boards as well as to the manufacturing method thereof.
2. Discussion of the Related Art
The lumber seasoning theory in the world is based on the premise in that natural water contained in vessels, capillary tubes, and cell cavities (comprising the lumber tissue) is unable to be uniformly liberated. Based on this theory, various lumber seasoning techniques have been established and various seasoning machines have been built. Lumber is a material that contracts as the water content decreases. If the liberating condition of the water contained in the tissue of the lumber differs, the rate of contraction differs from part to part. Consequently, lumber academies and the lumbering industry had knowledge that 1) lumber generates various deformations and warps in the lumber drying process and 2) deformation and warpage stop when the water contained in the lumber finishes being liberated, and 3) it is not possible to stop generation of deformations or cracks unless the drying is finished.
About 30 years ago, the inventor found that lumber 4 meters long by 300 mm square dried without generating deformations or cracks when the lumber was placed in a pressure vessel just after lumbering and pressurized and heated with saturated steam only once, and left as it was. This phenomenon occurs only when the lumber is pressurized and heated with saturated steam in a pressure vessel, but the inventor was unable to determine why this kind of phenomenon occurred. Therefore, the inventor thought that the basic premise of the lumber seasoning theory might be incorrect. The inventor then requested that Forestry Experiment Station of the Japanese Government Organization to conduct research into this subject. However, they did not make any research into this topic.
Another problem that remained unsolved was that the plant equipped with a pressure vessel installed a once-through boiler for the boiler. The steam pressure of about 3 kg/cm.sup.2 G was required for pressure of the saturated steam to be injected from the injection pipe inside the pressure vessel and the steam pressure was held constant by allowing the steam pressure generated in the boiler to pass the pressure reducing valve. However in the case of the once-through boiler, steam of various pressures was generated simultaneously due to the properties of the once-through boiler, and it was not possible to determine whether the steam of a pressure lower than 3 kg/cm.sup.2 G was generated or not. That is, the people did not understand that the once-through boiler is not worth while as a proper boiler, that is, it should not be used as a boiler.
Because the lumber academies have not realized that the premise of the conventional lumber seasoning theory is mistaken, there is a limit in lumber thickness that lumber manufacturers are able to season. Further, the lumber manufacturers continue to use a seasoning method that results in poor yield. They typically use a method of natural seasoning combined with hot-air seasoning and no attempt has been made to correct the actual conditions which generate enormous losses and aggravate global warming.